I was at a Scouts camp in Cornwall one brisk spring morning in 1960 when we heard that Caryl Chessman, a Californian robber and rapist, had finally been executed in the gas chamber at San Quentin jail after 12 years on death row. Years later, I discovered that my future Guardian boss, Ian Aitken – 84 this week – had been one of the reporters covering his last hours.

This time, the process has taken 22 years since Davis was convicted of the shooting of Mark MacPhail, an off-duty policeman trying to break up a brawl. Davis died still protesting his innocence – as he had during the long legal battle for his life during which key witnesses tried to withdraw their evidence as Ed Pilkington, at the prison in Jackson, as Aitken was at San Quentin 51 years ago, explains here in 10 crisp points.

A woman reporter who has witnessed 12 executions in the state (she practices detachment and always has a "very, very long shower" afterwards, she told Radio 4's Today programme) said she had not experienced such an outcry before.

She also sounded a bit perky for my taste, but seemed satisfied that the evidence against Davis was solid. To many people in many countries, that detail will matter. To others, the principle that capital punishment – the state taking lives in cold blood – is the only thing that matters and is wrong in any circumstances.

Broadly speaking, that is the European view nowadays, though the abolitionist movement has grown worldwide in recent decades – 96 countries have abolished the death penalty compared with 16 barely 30 years ago.

Russia is one of them, whereas the US (46 executions in 2010) and China – an estimated 5,000 – are not. Iran (252-plus) and North Korea (62-plus) are in the No 2 and No 3 spot, Muslim states being most conspicuous on the execution list. Japan executed two people.

Plenty of ironies to chew over in that list. Europe, the most godless continent, opposes capital punishment but is a world leader in promoting abortion. China, at least, has the consistency of supporting what some call the "double death" approach.

Today's Times carries a report on Davis's impending death but a more censorious and prominent one on Iran's execution of a 17-year-old – in public and from a crane.

Alireza Molla-Soltani had also been convicted of murder, killing a well-known athlete after a driving dispute as recently as July (they don't hang around with appeals in Iran). He claimed to have acted in self-defence and called out for his mother as the crowd cried: "Allah Akbar". His age – officials claimed he was 18 by their calendar – amounts to a breach of international law, critics say.

By coincidence (not?), President Mahmoud Ahmadinejad is due to address the UN general assembly today, his usual fiery anti-western rant, doubtless inflamed by persistent speculation that the clerical authorities who call the shots – and hangings – in Iran are getting fed up with his economic mismanagement.

We know the feeling, don't we? Also in New York, David Cameron's speech, the BBC reports in the adjoining item to Troy Davis's execution, will call on the international community to intervene more, Libya-style, "to stop repressive regimes from slaughtering their own people". Another irony there, then – it will probably go unremarked at Turtle Bay.

But examination of the Davis case requires several threads to be unpicked. Those who oppose capital punishment in all circumstances don't have a problem – it's always wrong. I don't take that view.

States and societies have reserved the right to execute people for a variety of crimes – from treason to stealing a loaf of bread – down the ages, and some still do. The pendulum of intellectual fashion, if I can call it that (I think I will) moves both ways over time, allowing everyone to take a turn at feeling superior.

In the US, the issue is one for the 50 states to decide, not a federal issue under the constitution of 1787. Most still do it occasionally, 14 (plus the District of Columbia) don't, mostly in the mid-west and north-east. Michigan alone never has done.

In Britain, abolitionists have been reducing the list of capital crimes for 200 years and had it suspended for murder in 1965 (mainland only), made permanent in 1969. The last offences – including treason – went in 1998, and the UK signed the 13th protocol of the European convention on human rights in 2003-4, so there the decision remains for the future.

During the course of the 20th century, we seem to have executed nearly 700 people. Were mistakes made? Of course, and it was Timothy John Evans's hanging in 1950 on the evidence of the serial murderer John Christie which crucially turned public opinion – and home secretaries – away from the practice. But the other side can argue, and does, that mistakes that allow killers to kill again also results in the deaths of innocents. It's a powerful point too.

In the case of Davis, things seem, if not straightforward, then at least to have a balance of propriety. Too many young – Davis was 20 at the time – African American men go to jail in the US and disproportionately too many go to the execution cell. Race is an aggravating factor, even now, and especially in the south, even now.

It's never wise to second-guess learned courts which have been through the evidence as the US supreme court – African American members included – has done and upheld the verdict of lower courts. Why has this case become a cause celebre when others do not? Perhaps because the weight of evidence against a safe conviction is, as Pilkington reports, so heavy. But perhaps for other reasons.

Beyond dispute is the idea that appeals can drag on for 20 years. Who benefits? Mostly lawyers, I imagine, though sometimes a reprieved or acquitted defendant. There are too many lawyers in America and not enough justice, I suspect. My sense is that justice might better have been served here by commutation – but American courts, like everyone else's, do not like to be told what to do by well-meaning foreigners.

An eloquent example of the search for justice surfaced this week in the person of former policeman John Murray, who cradled the dying Pc Yvonne Fletcher in his arms after she was shot by unknown Libyan official(s) from their London embassy in 1984.

The suspects were expediently allowed home, Blair-style, by Margaret Thatcher's government. But Murray promised his colleague he would find her killers and have them brought to justice.